Acetylcholine (ACh), a neurotransmitter substance, occurs in remarkable concentrations in noninnervated human placenta. ACh is present in placentae deriving from pregnancies of 6-7 weeks duration and undergoes characteristic fluctuations during the gestational period. Incomplete observations indicate ACh to be localized in a bound form in the trophoblast cells. It has been postulated that quantal ACh release controls permeability and transport processes across those cell layers which separate the fetal from the maternal circulation. The hypothesis of a cholinergic control of fetal growth will be examined with a bilaterally perfused single isolated cotyledon from human term placenta. This preparation allows us to study the transfer of isotopic analogues of natural metabolites (ions, amino acids, sugars, immunoproteins) and some drugs with known teratogenic effects in women (cytotoxic compounds, anticonvulsants) from the maternal to the fetal side and vice versa, before, during, and after the manipulation of the functional state of the cholinergic system by drugs which can alter synthesis, storage, release or hydrolysis of ACh when added to the perfusion fluids. Factors controlling release of ACh (ions: Ca ions, Mg ions, K ion; drugs: nicotine, narcotic analgesics, prostaglandins, titystoxin) will be examined. The relationship between ACh, cyclic 3',5'-guanosine monophosphate and the synthesis of proteohormones (chorionic somatomammotrophin and gonadotrophin) is to be tested.